So-called ultrahigh molecular weight ethylene-based polymers, which have extremely high molecular weight, are excellent in impact resistance, abrasion resistance, chemical resistance, strength and the like, as compared with general-purpose ethylene-based polymers, and thus have excellent characteristics as engineering plastics.
On the other hand, it is said that ultrahigh molecular weight ethylene-based polymers are not suitable for melt molding, which is a general resin molding method, because of their high molecular weight. For this reason, molding methods of ultrahigh molecular weight ethylene-based polymers have been developed such as a method in which an ultrahigh molecular weight ethylene-based polymer is dissolved in a solvent and molded, a solid-phase stretch-molding method in which the ultrahigh molecular weight ethylene-based polymer particles are stretched after compression-bonding at a temperature equal to or below the melting point of the polymer, and the like.
Patent Document 1 discloses that strength of the molded article molded by the solid-phase stretch-molding method using ultrahigh molecular weight polyethylene obtained using a post-metallocene catalyst described in Patent Document 2 ([3-t-Bu-2-O—C6H3CH═N(C6F5)]2TiCl2) becomes greater than or equal to 3 GPa. However, according to the polymerization method described in Patent Document 1, there is no use of a carrier, such as an inorganic solid component and the like, for support of the aforementioned catalyst component. Thus, during the polymerization reaction, it is anticipated that there will be the occurrence of the phenomenon of attachment of the polymer to the polymerization reactor walls, agitator blades, or the like, i.e. so-called fouling. It is therefore assumed that stable industrial production would be extremely difficult using the ethylene-based polymer production method described in Patent Document 1. Furthermore, a large amount of expensive organoaluminumoxy compound is required as a co-catalyst in order to exert high catalytic activity in this method. Thus a separate deashing step becomes necessary in order to remove the inorganic components contained in the polymer, and it is anticipated that cost will become extremely high during industrial production.
On the other hand, suppression of fouling in production of an ultrahigh molecular weight ethylene-based polymer is possible by use of a supported type catalyst such as a titanium-based supported type catalyst using a magnesium compound as a support as described in Patent Documents 3, 4, or the like, or, by use of a supported type catalyst in which a transition metal compound is supported on an inorganic solid component formed from SiO2 treated with an organoaluminumoxy compound as described in Patent Document 5, or the like. Industrial production is known to be possible due to the ability to suppress fouling by the use of a supported type catalyst. However, a molded article with sufficient strength is not obtained using the ultrahigh molecular weight ethylene-based polymer particles produced using this type of supported type catalyst, even when the ultrahigh molecular weight ethylene-based polymer particles are solid-phase stretch-molded (Patent Document 6 or the like).